Organic light emitting display with improved light emitting efficiency

ABSTRACT

An organic light emitting display includes an anode; an organic layer on the anode; and a cathode on the organic layer. The cathode includes a first region and a second region which are sequentially disposed on the organic layer in parallel. The first and second regions are formed by doping a metal oxide on an indium oxide matrix. The doping density of the metal oxide of the first region is greater than that of the second region, the metal oxide of the first region has a density gradient, and the density of the metal oxide in a boundary surface of the first and second regions is the same. An organic light emitting display according to the present invention can increase light emitting efficiency without using a resonance structure.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2008-0081363, filed in the Korean IntellectualProperty Office on Aug. 20, 2008, the entire content of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an organic light emitting displayhaving a top-emission structure with improved light emitting efficiency.

BACKGROUND OF THE INVENTION

Organic light emitting displays are self-emission devices. Organic lightemitting displays have higher luminescence than liquid crystal displays,and are thinner than liquid crystal displays, as organic light emittingdisplays do not include a backlight unit.

An organic light emitting display has a structure wherein an anode, anorganic layer, and a cathode are sequentially stacked on a substrate onwhich a pixel circuit, such as a thin film transistor, is deposited. Thestructure of an organic light emitting display can be a top-emissionstructure or a bottom-emission structure. In a top-emission structure,an image is realized toward the opposite direction of the depositedsubstrate, i.e., toward the cathode, and thus the aperture ratio of thetop-emission structure is higher than that of the bottom-emissionstructure where an image is realized toward the substrate. Accordingly,the light emitting efficiency of a top-emission organic light emittingdevice is higher than a bottom-emission organic light emitting device.However in the top-emission structure, the cathode must be transparent,which is difficult. Generally, a basic requirement of the cathode isthat the cathode must have a lower work function than the anode, but amaterial having a low work function is generally a metal that has lowlight transmittance.

A conventional transparent cathode is created by forming a thin metallayer having a low work function, but the light transmittance is stillvery low, and it is difficult to improve light transmittance.

Due to this limitation, a micro-cavity that amplifies light emitted froman emission layer has been suggested. However, the optimum thicknessesof micro-cavities are different for each color, and thus the thicknessof the organic layer disposed between the anode and the cathode aredifferent for each color. In other words, in an organic light emittingdisplay, light is emitted as excitons are formed in the organic emissionlayer as electrons are injected into the holes of the anode from thecathode. In order to adjust the distance from the excitons and theresonance thickness, the thickness of the organic layer, specificallythe thicknesses of the hole or electron injection layer, or the hole orelectron transport layer, must be varied. Because the thickness of theorganic layer must be different for each color, independent masks areused for each color. However, such an independent depositing method iscomplex, and thus the production costs increase.

Also, to increase the resolution of a display, masks must have a higherresolution pattern, which is difficult to obtain in a large areadisplay.

Moreover, the thickness of the organic layer cannot be determined basedonly on the optical efficiency, because when the thickness of holelayers or electron layers are different, electrical characteristics ofthe organic light emitting display may deteriorate.

SUMMARY OF THE INVENTION

An embodiment of the present invention includes a top-emission typeorganic light emitting display comprising a cathode that is transparentand has a low work function, so as to increase the light emittingefficiency without employing a resonance structure in realizing an imagetoward the cathode.

In an embodiment of the present invention, an organic light emittingdisplay includes: an anode; an organic layer on the anode, whichincludes an emission layer; and a cathode which is formed on the organiclayer and transmits light emitted from the emission layer of the organiclayer. The cathode includes a first region and a second region which aresequentially disposed on the organic layer in parallel. The first andsecond regions are formed by doping a metal oxide on an indium oxidematrix. The doping density of the metal oxide of the first region isgreater than that of the second region, the metal oxide of the firstregion has a density gradient, and the density of the metal oxide in aboundary surface between the first and second regions is the same.

In embodiments of the present invention, a metal of the metal oxide maybe Cs, Ca, Sr, Ba, Y, or a lanthanoid element.

In embodiments of the present invention, the doping density of the metaloxide may be a linear function with respect to a distance between thefirst region and the organic layer.

In embodiments of the present invention, the maximum value of the dopingdensity of the metal oxide in the first region of the cathode may befrom about 2% to about 10%.

In embodiments of the present invention the doping density of the metaloxide of the second region may be from about 0.0% to about 2.0%.

In embodiments of the present invention the average doping density ofthe metal oxide of the cathode may be from about 0.5% to about 12%.

In embodiments of the present invention, the thickness of the firstregion may be from about 5 nm to about 50 nm.

In embodiments of the present invention, the thickness of the secondregion may be from about 50 nm to about 200 nm.

In embodiments of the present invention, the thickness of the entirecathode may be from about 70 nm to about 200 nm.

In embodiments of the present invention, the work function of the firstregion may be between 3.6 eV and 4.7 eV.

In embodiments of the present invention, the resistivity of the secondregion may be from about 2.5 Ωm to about 4.5 Ωm.

In embodiments of the present invention, light transmittance of thecathode may be from about 80% to about 95%.

In embodiments of the present invention, a method of manufacturing anorganic light emitting display includes: forming an anode; forming anorganic layer including an emission layer on the anode; and forming acathode on the organic layer, wherein the cathode is a transparentconductive layer. The cathode is comprised of a first region and asecond region, sequentially formed on the organic layer in parallel. Thecathode is formed by doping a metal or a metal oxide on an indium oxideby thermal depositing the metal or the metal oxide and the indium oxidewhile plasma is formed in a chamber. The first layer is formed byadjusting the doping amount of the metal or the metal oxide to decreaseor increase according to a gradation deposition method, and a secondregion is formed on the first layer by fixing the doping amount of themetal or the metal oxide to be uniform.

In embodiments of the present invention, the metal may be Cs, Ca, Sr,Ba, Y, or a lanthanoid element.

In embodiments of the present invention, in forming the cathode, thermaldeposition using metal and indium sources may be performed in an oxygenatmosphere.

In embodiments of the present invention, in forming the cathode, thermaldeposition may be performed using metal and indium as sources in anatmosphere wherein oxygen and argon are mixed.

In embodiments of the present invention, the thermal deposition may beperformed at a temperature equal to or below 100° C.

In embodiments of the present invention, in forming the cathode, thethermal deposition may be performed by ion beam assisted deposition.

In embodiments of the present invention, ions emitted from an ion beamsource used in the ion beam assisted deposition may be ions of inertatoms.

In embodiments of the present invention, energy of the ion beam sourceused in the ion beam assisted deposition may be from about 50 eV toabout 200 eV.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view illustrating an active matrix typeorganic light emitting display according to an embodiment of the presentinvention;

FIG. 2 is a cross-sectional view illustrating an active matrix typeorganic light emitting display according to another embodiment of thepresent invention;

FIG. 3 is a diagram illustrating a cathode manufactured on a glasssubstrate according to an embodiment of the present invention;

FIG. 4 is a graph comparing light transmittances of cathodes accordingto embodiments of the present invention and the light transmittance of aconventional cathode;

FIG. 5 is a graph of work function according to a calcium depositionrate (Ca DR) when manufacturing a calcium doped cathode according toembodiments of the present invention; and

FIG. 6 is a diagram schematically illustrating principles of ion beamassisted deposition (IBAD).

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described more fully with reference to theaccompanying drawings, in which exemplary embodiments of the inventionare shown.

FIG. 1 is a cross-sectional view illustrating an active matrix typeorganic light emitting display 60 according to an embodiment of thepresent invention, illustrating a capacitor 50 and a thin filmtransistor (TFT) 40.

Referring to FIG. 1, the organic light emitting display 60 includes asubstrate 81. The substrate 81 may be formed of a transparent material,such as glass or plastic. A buffer layer 82 is formed on the substrate81. The capacitor 50 includes a first capacitor electrode 51 and asecond capacitor electrode 52 on the buffer layer 82.

An active layer 44 arranged in a pattern is formed on the top surface ofthe buffer layer 82. The active layer 44 is covered by a gate insulationlayer 83. The active layer 44 may be a p-type or an n-typesemiconductor.

A gate electrode 42 of the TFT 40 is formed on the top surface of thegate insulation layer 83 corresponding to the active layer 44. The gateelectrode 42 is covered by an intermediate insulation layer 84. Afterthe intermediate insulation layer 84 is formed, contact holes 83 a and84 a are formed in the glass insulation layer 83 and the intermediateinsulation layer 84 by etching the gate insulation layer 83 and theintermediate insulation layer 84 using an etching process such as dryetching, thereby exposing portions of the active layer 44.

The exposed portions of the active layer 44 are each connected to asource electrode 41 and a drain electrode 43 of the TFT 40, formed inthe predetermined pattern, using the contact holes 83 a and 84 a. Thesource electrode 41 and the drain electrode 43 are covered by aprotective layer 85. After the protective layer 85 is formed, a part ofthe drain electrode 43 is exposed using an etching process.

The protective layer 85 may be an insulator and formed of an inorganicmaterial such as a silicon oxide or a silicon nitride, or an organicmaterial such as acryl or benzocyclobutene (BCB). Also, a separateinsulation layer (not shown) may be further formed on the protectivelayer 85 for planarizing the protective layer 85.

The organic light emitting display 60 displays an image by emitting red,green, and blue according to flow of the currents. The organic lightemitting display includes an anode 61, which is a pixel electrodeconnected to the drain electrode 43 of the TFT 40, a cathode 62, whichis a counter electrode covering entire pixels, and an organic layer 63,which is disposed between the anode 61 and the cathode 62 and includesan emission layer (not shown) emitting light. A pixel defining layer 86covering the anode 61 includes a pixel opening 64 that exposes a portionof the anode 61.

The anode 61 and the cathode 62 are insulated from each other, and applyvoltages of different polarities to the organic layer 63 to emit light.

The organic layer 63 may be formed of a low molecular organic materialor a high molecular organic material. When a low molecular organicmaterial is used, a hole injection layer (HIL), a hole transport layer(HTL), an emission layer (EML), an electron transport layer (ETL), andan electron injection layer (EIL) may be stacked in a single or complexstructure. Examples of suitable low molecular organic materials includecopper phthalocyanine (CuPc),N,N′-Di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB), andtris-8-hydroxyquinoline aluminum (Alq3). The organic layer comprisinglow molecular organic material may be formed using a vacuum depositionmethod.

When the high molecular organic material is used, an HTL and an EML maybe stacked. The HTL may be comprised of Poly(3,4-ethylenedioxythiophene)(PEDOT) and the EML may be comprised of poly-phenylenevinylene (PPV) orpolyfluorene high molecular organic material. The HTL and the EML may beformed using a screen printing or an inkjet printing method. However,the organic layer 63 is not limited to the above examples.

The anode 61 may be patterned to correspond to areas of each pixel, andthe cathode 62 may cover all pixels.

The anode 61 may be transparent or reflective. When the anode 61 istransparent, the anode 61 may be formed of indium tin oxide (ITO),indium zinc oxide (IZO), zinc oxide (ZnO), or indium oxide (In₂O₃). Whenthe anode 61 is reflective, a reflective layer may be formed using Ag,Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, or mixtures thereof. A transparentelectrode layer may then be formed on the reflective layer using ITO,IZO, ZnO, or In₂O₃.

The cathode 62 is formed to be transparent by doping a calcium oxide onan indium oxide matrix. The doping density of calcium in the cathode 62may vary.

A material used to form a transparent cathode must have hightransmittance in a visible ray area and a low work function for suitableelectric conductivity for use as an electric material and convenientelectron injection to an organic material. Generally, the transmittanceof a visible ray from a metal to an insulator increases while electricconductivity from a metal to an insulator decreases. Mg/Ag, Al/Li,Yb/Ag, and Ca/Ag, which are well known cathode materials, have excellentelectric characteristics and work function. However, when the thicknessof a cathode made of these metals is equal to or above 10 nm, thetransmittance is about 30%, and thus a light emitting efficiency oflight emitted from an organic light is reduced. Furthermore, due to theuse of a metal electrode, a resonance structure is generated, and thusthe process is unstable, the driving voltage is increased, and thematerial cost is increased.

When metal is doped on a thin layer of ITO or ZnO to be used as atransparent electrode, the work function is equal to or higher thanabout 5.0 eV. Due to the high work function, such a transparentelectrode may be unable to be used.

The cathode 62 according to an embodiment of the present invention is atransparent electrode including a metal oxide, and is formed in such away that a doping density of the metal oxide has a density gradient soas to control the work function. In other words, the doping density ofthe metal oxide close to the organic layer 63 is higher so as todecrease the work function, and lower when the metal oxide is far fromthe organic layer 63 so that the cathode 62 becomes transparent.

The cathode 62 may be divided into two regions, i.e., a first regionwherein the doping density of the metal oxide is higher near the oxidelayer 63, and a second region wherein the doping density of the metaloxide is uniformly maintained but lower than that of the first region.

The metal oxide may be an oxide of Cs, Ca, Sr, Ba, Y, or a lanthanoidelement. As used herein, lanthanoid elements are those elements havingan atomic number of 57 to 71.

In FIG. 2, the cathode 62 is divided into a first region 62 a and asecond region 62 b. The doping density of the metal oxide on theboundary surface of the first and second regions 62 a and 62 b is thesame. Furthermore, the first and second regions 62 a and 62 b are notformed as two separate layers, but are formed as a single layer having adensity gradient.

The doping density of the metal oxide in the first region 62 a decreasesfrom the surface contacting the organic layer 63 towards the secondregion 62 b. The doping density of the metal oxide of the first region62 a may decrease linearly with respect to the distance from the surfacecontacting the organic layer 63.

The doping density of the metal oxide in the first region 62 a may be ata maximum in the surface contacting the organic layer 63. The maximumdoping density of the first region may be from about 2% to about 10%.When the maximum doping density of the first region exceeds 10%, lighttransmittance may deteriorate, and when the maximum doping density ofthe first region is below 2%, the work function may deteriorate.

Meanwhile, the doping density of the metal oxide in the second region 62b may be the minimum value of the doping density of the metal oxide inthe first region 62 a. The doping density of the second region may befrom about 0.0% to about 2.0%. When the doping density of the secondregion exceeds 2%, resistance may deteriorate.

The average doping density of the metal oxide in the cathode 62 may bebetween 0.5% and 12%. When the average doping density of the cathodeexceeds 12%, the resistance may deteriorate, and when the average dopingdensity of the cathode is below 0.5%, the work function may deteriorate.

The thickness of the first region 62 a may be from about 5 nm to about50 nm. When the thickness is below 5 nm, a low work function may not beobtained, and when the thickness exceeds 50 nm, a low resistance may notbe obtained.

The thickness of the second region 62 b may be from about 50 nm to about200 nm. When the thickness is below 50 nm, a low resistance may not beobtained, and when the thickness exceeds 200 nm, a low work function maynot be obtained.

The entire thickness of the cathode 62 may be from about 70 to about 200nm. When the thickness is below 50 nm, a low resistance may not beobtained, and when the thickness exceeds 200 nm, a low work function maynot be obtained.

According to an embodiment of the present invention, the work functionof the first region 62 a may be adjusted to be from about 3.6 eV toabout 4.7 eV, by adjusting the doping densities of the metal oxides andthicknesses of the first and second regions 62 a and 62 b. Theresistivity of the second region 62 b may be from about 2.5 Ωm to about4.5 Ωm. The light transmittance of the cathode 62 may be from about 80%to about 95%.

As described above, according to an embodiment of the present invention,the light transmittance of the cathode 62 is remarkably increased, andthus the light emitting efficiency may not be further improved byapplying a resonance structure. Accordingly, the organic light emittingdisplay 60 may use a non-resonance structure, thereby having an improvedview angle characteristic and may also exclude an optical structure inthe organic light emitting display 60.

An auxiliary electrode layer (not shown) or a bus electrode line (notshown) may be optionally formed on the cathode 62 by using ITO, IZO,ZnO, or In₂O₃. However, in an embodiment of the present invention, thecathode 62 comprises only a thin layer formed on the organic layer 63.One of ordinary skill in the art would know how to include an electrodelayer or a bus electrode line in embodiments of the present invention.

A protective layer 65 may be further formed on the cathode 62. In otherembodiments, a capping layer 67 may be between the protective layer 65and the cathode 62.

An embodiment of the present invention provides a method ofmanufacturing an organic light emitting display, the method includingforming an anode, forming an organic layer including an emission layeron the anode, and forming a cathode on the organic layer. To form thecathode, a transparent conductive layer, a metal or a metal oxide isdoped on an indium oxide by thermal depositing the metal or the metaloxide and the indium oxide while plasma is formed in a chamber. A firstlayer of the cathode is formed by adjusting the doping amount of themetal or the metal oxide to decrease or increase according to agradation deposition method, and then a second region of the cathode isformed by fixing the doping amount of the metal or the metal oxide to beuniform. The first and second regions are sequentially formed on theorganic layer in parallel.

An organic light emitting display 60 may be manufactured according tothe above method.

In an embodiment of the present invention the anode may be formed usingvarious methods such as a deposition method or a sputtering method. Inother words, referring to FIGS. 1 and 2, the organic layer 63 is not yetformed when the anode 61 is formed, and thus the anode 61 may be formedusing any method.

The organic layer 63 may be formed on the anode 61 using a vacuumdeposition method or the like.

The cathode 62 is formed on the organic layer 63 as a transparentconductive layer. The cathode 62 is a transparent conductive layerwherein a metal oxide is doped on an indium oxide. Conventionally, thecathode 62 is formed using a sputtering method. However, if a cathode isformed using a sputtering method in embodiments of the presentinvention, the organic layer 63 is damaged due to characteristics of thesputtering method. When a cathode 62 is formed using a thermaldeposition method in embodiments of the present invention, the organiclayer 63 is damaged due to high temperature during thermal deposition.However, according to embodiments of the present invention, the cathode62 is formed using low temperature thermal deposition, and thus theorganic layer 63 is not damaged. Accordingly, an organic light emittingdisplay 60 having high quality is manufactured.

When the cathode 62 is formed using the thermal deposition method, thetemperature of the substrate 81 on which the organic light emittingdisplay 60 is to be formed reaches about 300° C., and thus the organiclayer 63, as an intermediate layer, is damaged by the high temperature.According to embodiments of the present invention, a metal oxide and anindium oxide are thermal deposited while plasma is formed in a chamber,remarkably reducing the temperature of the substrate 81. In other words,the cathode 62 is formed while plasma is formed in the chamber, ionizinga material of the cathode 62, so that deposition is formed withoutincreasing the deposition temperature. As such, when the cathode 62 isthermal deposited while plasma is formed in the chamber, the temperatureof the substrate 81 only increases up to 100° C., and thus the organiclayer 63 is not damaged. Also, when the cathode 62 is thermal depositedwhile plasma is formed in the chamber, the temperature of the substrate81 is reduced, and mobility of the cathode 62 is improved, and thusresistance of the cathode 62 is remarkably reduced.

As described above, the organic layer 63 disposed between the anode 61and the cathode 62 includes not only the emission layer but also othervarious layers such as an EIL, an ETL, an HIL, and an HTL. The othervarious layers are formed of materials having a suitable lowestunoccupied molecular orbital (LUMO) level, in consideration of the workfunctions of the anode 61 and the cathode 62. Accordingly, in order touse conventional materials for an organic layer, the work function ofthe cathode of an organic light emitting display manufactured using themethod of an embodiment of the present invention may have a similar workfunction as a transparent cathode manufactured using a conventionalsputtering method.

In an embodiment of the present invention, an indium oxide is thermaldeposited simultaneously with a metal or a metal oxide, instead ofthermal depositing only an indium oxide while forming the cathode 62.The cathode 62 is divided into two regions having different dopingdensities of a metal oxide.

FIG. 3 is a diagram illustrating a cathode manufactured on a glasssubstrate according to an embodiment of the present invention. In FIG.3, the cathode is formed in a single layer, but the density of a metalin the cathode may be controlled as the cathode is formed using agradation deposition method. The gradation deposition method may be, forexample, a method of changing a deposition rate of a metal while fixinga deposition rate of an indium oxide.

FIG. 3 illustrates the cathode deposited on glass in a single layerform. A first region directly on the glass is deposited by decreasing adeposition rate of a metal in the gradation deposition method. Then, asecond region is deposited while uniformly maintaining a low depositionrate of the metal so as to support a high resistance in the firstregion.

The glass of FIG. 3 is for illustration and testing purposes only, as inembodiments of the present invention, the cathode is formed on theorganic layer 63 of FIG. 1 or 2.

In embodiments of the present invention, a metal or a metal oxide and anindium oxide are simultaneously thermal deposited to form the cathode.The metal may be Cs, Ca, Sr, Ba, Y, or a lanthanoid element. The metaloxide may be cesium oxide, calcium oxide, strontium oxide, barium oxide,yttrium oxide, or oxides of a lanthanoid element. An absolute value ofthe work function of the metal or the metal oxide is lower than anabsolute value of the work function of the indium oxide.

A method of forming such a cathode, i.e. a method of forming atransparent conductive layer wherein the metal oxide is doped on theindium oxide, may vary. For example, thermal deposition may be performedin an oxygen atmosphere or an oxygen and argon mixed atmosphere, havingmetal and indium as sources. In this case, due to the oxygen atmosphere,the indium turns into an indium oxide and the metal turns into a metaloxide, and thus, as a result, the cathode, wherein the metal oxide isdoped on the indium oxide, is formed. Alternatively, the thermaldeposition may be performed in an oxygen atmosphere or an oxygen andargon mixed atmosphere having a metal and an indium oxide as sources. Inthis case, the metal turns into a metal oxide in the oxygen atmosphere,and thus the cathode, wherein the metal oxide is doped on the indiumoxide, is formed. Alternatively, the thermal deposition may be performedin an argon atmosphere having a metal oxide and an indium oxide assources, thereby forming the cathode wherein the metal oxide is doped onthe indium oxide. In this case, since argon is an inactive gas, argondoes not affect the metal oxide or the indium oxide.

FIG. 4 is a graph comparing light transmittances of cathodes formedusing a method according to embodiments of the present invention and aconventional cathode. Cathodes formed by using a method according toembodiments of the present invention have a thickness of 1000 Å and, fortesting purposes, are formed by depositing calcium as a metal on a glassat deposition rates of 0.5 Å/s and 0.6 Å/s. The calcium is doped in aform of a calcium oxide after being combined to oxygen, and thus thetransmittance of the calcium is similar to transmittance of indiumoxide. Accordingly, transmittance is similar regardless of the dopingamount of calcium. Meanwhile, the conventional cathode has a thicknessof 160 Å and is formed by co-depositing Mg and Ag. Referring to FIG. 4,the transmittance of a conventional cathode is about 33%, whereas thetransmittances of the cathodes formed by using a method according toembodiments of the present invention are equal to or higher than about85%. Accordingly, it can be seen that the transmittances of cathodesformed by using the methods of embodiments of the present invention areimproved compared to the transmittance of conventional cathodes.

FIG. 5 is a graph of a work function according to a calcium depositionrate (Ca DR), when calcium is used as a metal in the first region ofFIG. 3. When CaO is formed, as the calcium is combined to oxygen, workfunction decreases. According to V. S. Fomenko, Handbook of ThermoionicProperties, Plenum Press Data Division (New York, 1966), work functionsof Cs, Sr, Ba, Y, and lanthanoid elements, like the work function of Ca,decrease when oxidized. Work functions of pure metals do not decreasewhen pure metals are oxidized. As shown in FIG. 5, as the amount of CaOincreases, the work function decreases. For example, when the Ca DR is0.6, the work function is 4.4 eV.

As the Ca DR is high during initial deposition, a work function on theinterface between the glass of FIG. 3 and a deposited thin layer cathodemay be lower than the work function of the deposited thin layer cathodeas a whole. The resistivity at the interface between the glass of FIG. 3and the deposited thin layer cathode is 3˜20×10⁻⁴ Ωm.

The cathode 62 of FIG. 1 or the first or second region 62 a or 62 b ofFIG. 2 may be formed by ion beam assisted deposition (IBAD) using anevaporation source and an ion beam source.

FIG. 6 is a diagram schematically illustrating IBAD. Referring to FIG.6, particles 92 are discharged from an evaporation source 97, and aredeposited on one surface of a substrate 91. Meanwhile, ions 93 aredischarged from an ion beam source 95, increasing the surface mobilityof the particles 92, and thus the particles 92 are densely deposited onthe substrate 91.

According to a method of manufacturing an organic light emitting displayaccording to an embodiment of the present invention, a cathode may beformed by using IBAD.

Specifically, when the second region 62 b of FIG. 2 is formed by usingIBAD, the first region 62 a may be formed first by using a conventionaldeposition method, such as a vacuum deposition method or a thermaldeposition method. Then, the second region 62 b may be formed by usingIBAD on the first region 62 a. In this case, the first and secondregions 62 a and 62 b of the cathode 62 are formed of the same material,but since the first and second regions 62 a and 62 b are formed usingdifferent methods, atom arrangement structures of the first and secondregions 62 a and 62 b are different.

The particles 92 discharged from the evaporation source 97 during IBADare materials for forming the cathode 62, and may be indium, an indiumoxide, a metal, or a metal oxide, as described above.

Meanwhile, the ions 93 discharged from the ion beam source 95 generallydo not react with the substrate on which the cathode 62 is formed, theorganic layer 63, or the particles 92 discharged from the evaporationsource 91. The ions 93 may be ions of an inert atom, for example, Ar⁺,Kr⁺, or Xe⁺ ions.

Energy of the ion beam source 95 ranges between 50 eV and 200 eV, andmay range between 80 eV and 150 eV. When the energy is below 50 eV, thesurface mobility of the particles 92 cannot be increased as the energyof the ions 93 too low, and thus the cathode 62 having a high densityand low surface illuminance may not be formed. When the energy exceeds200 eV, the cathode 62 may be etched since the energy of the ions 93 istoo high. In some embodiments of the invention, the energy may be 150eV.

In using IBAD, the ratio of the number of particles 92 discharged fromthe evaporation source 97 to the number of ions 93 discharged from theion beam source 95 may range between 1:1 and 0.9:1 (particles:ions). Insome embodiments of the present invention, the ratio of particles 92discharged from the evaporation source 97 to the number of ions 93discharged from the ion beam source 95 may be 0.9:1. When the number ofions 93 exceeds the 0.9:1 ratio, the cathode 62 may be etched by theions 93. When the number of ions 93 is below the 1:1 ratio, the surfacemobility of the particles 92 may not be increased by the ions 93, andthus the cathode 62 having a compact structure in a high density and alow surface illuminance may not be formed.

The ratio of particles to ions may be varied by controlling the electronflow rate of the ion beam source 95 or the inflow rate of ion generatinggas. For example, when an Al cathode is formed by using an evaporationsource discharging Al particles and an ion beam source discharging argonions, the ion flow rate of the ion beam source can be adjusted to 50 mAand the inflow rate of argon gas can be adjusted to 5 sccm. In such acathode, the ratio of Al particles to argon ions is 1:1.

In using IBAD, a thermal evaporation source or an electro evaporationsource is used as the evaporation source 97. The ion beam source 95 maybe a Kaufmann type ion gun, an End-Hall type ion gun, or an RF type iongun. One of ordinary skill in the art may select any evaporation source97 and ion beam source 95 that is suitable for IBAD.

The organic light emitting display of the present invention is an activematrix organic light emitting display, but the present invention is notlimited thereto.

The present invention will now be described in further detail withreference to the following examples.

EXAMPLE 1

An organic light emitting display having an anode/organic layer/cathodestructure was formed on a TFT as described above. In Example 1, thecathode was formed using IBAD. The ion beam used in the IBAD had avoltage of between 50 V and 200 V, and a current of between 0.05 A and0.2 A.

A glass substrate, wherein 1500 Å of ITO, 400 Å of4,4′-bis(N-(4-(N-(3-methylphenyl)-N-phenylamino)phenyl)-N-phenylamino)biphenyl(DNTPD), 150 Å of NPB, 300 Å of distyrylanthracene (DSA)+5%distyrylanthraceneamine (DSAamine), 100 Å ofbis(10-hydroxybenzo[h]quinolinato beryllium (Bebq2), and 10 of Å LiFwere sequentially stacked on the substrate. A first layer of a cathodewas formed having a thickness between 20 nm and 30 nm, by depositingcalcium at an initial deposition rate of 0.7 Å/s, until the depositionrate decreased to 0.2 Å/s. Then, a second region of the cathode wasformed having a thickness between 60 nm and 100 nm, by maintaining thedeposition rate of calcium between 0.0 Å/s and 0.2 Å/s. An Al depositionsource was prepared by using an Al wire having a diameter of 3π. Next, acontainer including the Al deposition source, an ion beam source, athermal evaporation source, a substrate holder, and a rotation shaftthat rotates the substrate holder was prepared. An End-Hall type ion gun(manufactured by Infovion, Inc., Korea) was used as the ion beam source,and a Helisys (manufactured by ANS, Inc., Korea) was used as the thermalevaporation source. After mounting the substrate on the substrate holderthat faces the Al deposition source, the container was operated so as toform an Al layer having a thickness of 2000 Å on the substrate under theconditions shown in Table 1 below.

TABLE 1 Basic Pressure 1.0 × 10⁻⁷ Torr Gas Flow Rate Oxygen Flow Rate:−2 sccm Argon Flow Rate: −10 sccm Thermal Evaporation Source TungstenBoat, BN Boat Thermal Evaporation Source 200 A Operation Condition IonBeam Source End-Hall Type Ion Gun Ion Beam Source Operation ConditionDischarge Current: −500 mA Discharge Voltage: −300 V Beam Voltage: −150eV Beam Current: −50 mA Depositon Angle 90° Substrate RPM 4.5 SubstrateTemperature 80° C. Deposition Rate 5 Å/sec

An organic light emitting display including the Al layer formed inExample 1 is referred to as Sample 1.

COMPARATIVE EXAMPLE 1

An organic light emitting display, wherein 1500 Å of ITO, 400 Å ofDNTPD, 150 Å of NPB, 300 Å of DSA+5% DSAamine, 100 Å of Bebq2, 10 Å ofLiF, and 1500 Å of Al were sequentially stacked on a glass substrate inthe same manner as in Example 1. The organic light emitting display madeaccording to Comparative Example 1 is referred to as Comparative Sample1

EVALUATION

Current-voltage characteristics of Sample 1 and Comparative Sample 1were evaluated by using a Keithley 238 source-measure unit (manufacturedby Keithley Instruments, Inc.; Cleveland, Ohio). Sample 1 had anexcellent current density characteristic and an excellent efficiencycharacteristic compared to Comparative Sample 1.

The current efficiency of Sample 1 was measured, and a currentefficiency of 5 cd/A was detected at 5 V, which demonstrates that Sample1 has excellent electric characteristics.

As described above, an organic light emitting display having atop-emission structure can have an increased light coupling efficiencywithout employing a micro-cavity structure. Additionally, an organiclight emitting display having a top-emission structure can have adecreased driving voltage.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. An organic light emitting display comprising: ananode; an organic layer on the anode comprising an emission layer; and acathode on the organic layer, wherein the cathode comprises a firstregion adjacent to the organic layer and a second region adjacent to thefirst region, the first and second regions comprising an indium oxidematrix doped with a metal oxide wherein: a doping density of the metaloxide of the first region is greater than a doping density of the metaloxide of the second region; the doping density of the metal oxide of thefirst region has a doping density gradient; the doping density of themetal oxide of the second region is uniform; and the doping densities ofthe metal oxide at a boundary surface between the first region and thesecond region are the same.
 2. The organic light emitting display ofclaim 1, wherein a metal of the metal oxide is selected from the groupconsisting of Cs, Ca, Sr, Ba, Y, and lanthanoid elements.
 3. The organiclight emitting display of claim 1, wherein the doping density gradientof the metal oxide of the first region has a linear relationship withrespect to a distance from the organic layer.
 4. The organic lightemitting display of claim 1, wherein the maximum value of the dopingdensity of the metal oxide in the first region of the cathode is fromabout 2% to about 10%.
 5. The organic light emitting display of claim 1,wherein the doping density of the metal oxide of the second region isless than about 2.0%.
 6. The organic light emitting display of claim 1,wherein the average doping density of metal oxide of the cathode is fromabout 0.5% to about 12%.
 7. The organic light emitting display of claim1, wherein the thickness of the first region is from about 5 nm to about50 nm.
 8. The organic light emitting display of claim 1, wherein thethickness of the second region is from about 50 nm to about 200 nm. 9.The organic light emitting display of claim 1, wherein the thickness ofthe cathode is from about 70 nm to about 200 nm.
 10. The organic lightemitting display of claim 1, wherein a work function of the first regionis between about 3.6 eV and about 4.7 eV.
 11. The organic light emittingdisplay of claim 1, wherein a resistivity of the second region is fromabout 2.5 Ωm to about 4.5 Ωm.
 12. The organic light emitting display ofclaim 1, wherein light transmittance of the cathode is from about 80% toabout 95%.